A digital subscriber line (DSL) technology is a high-speed transmission technology in which data is transmitted by using a telephone line, that is, an unshielded twisted pair (UTP). A DSL system has a plurality of DSL lines, a DSL access multiplexer (DSLAM) usually provides an access service for the plurality of DSL lines. The DSL line is also referred to as a subscriber line.
ITU-T Q4 uses time division duplexing (TDD) as a duplex manner of a next-generation copper wire broadband access standard Gfast. However, due to an electromagnetic induction principle, mutual interference, referred to as crosstalk, is generated between a plurality of signals that gain access to the DSLAM. As a frequency band used by Gfast becomes wider, far-end crosstalk (FEXT) more severely affects transmission performance of a line, and the crosstalk of a twisted pair is extremely strong at a high frequency. To cancel the crosstalk, a vectoring DSL technology may be used to cancel the far-end crosstalk.
For the vectoring technology, joint sending and joint receiving among lines are mainly performed at a DSLAM end to cancel FEXT interference by using a signal processing method, and finally the FEXT interference is canceled in each signal.
When the vectoring technology is used in a Gfast system, and a precoder coefficient does not change in a downstream direction, all subscriber lines in a vectoring group need to simultaneously perform signal sending, and when there is no service data to send on some of the subscriber lines, a precoder output signal still needs to be sent on those subscriber lines. When a backward canceller coefficient does not change in an upstream direction, all the subscriber lines in the vectoring group need to simultaneously perform signal receiving even though subscriber ends of some of the subscriber lines have no service data to send. In addition, the Gfast system is a high bandwidth system at a rate of 1 Gbps in a typical scenario. In an actual application, service data traffic of each subscriber line greatly changes. Due to a constraint of simultaneous joint sending and receiving, a large quantity of idle symbols are filled in a transmission timeslot of the system, and consequently, energy consumption is wasted.